Anniversary of the October 3, 1979 Windsor Locks, CT F4 Tornado

One of the strongest recorded tornadoes in CT history (perhaps only outdone by the Wallingford tornado of 1878 which is estimated to be F4) occurred at Bradley International Airport on Wednesday, October 3, 1979. The killer tornado was rated as a high-end F4 tornado. Not only are violent tornadoes extremely unusual in CT (the only other tornado to achieve an F4 rating was the Hamden tornado which occurred July 10, 1989. Note: The F-scale did not exist in 1878 so the rating is estimated based off damage reports), but the time of year made this tornado extremely unusual. Below, we will explore the science and meteorology behind the F4 tornado of October 3, 1979.

Meteorological Set-up:

The synoptic pattern was characterized by a large ridge across the western United States with a trough digging into the eastern United States. The graphic below displays 500mb (~18,000 feet above our heads) height anomalies across the United States on Tuesday, October 2, 1979. The yellows and reds indicate above-average heights; indicative of a ridge while the blues and purples indicate below-average heights; indicative of a trough:

In the days preceding October 3, 1979, a ridge was building across the western United States with a trough configured across the east. This troughing was only enhanced by a rather significant trough digging into the northern Plains on the morning of October 3. Within the initial trough was a vigorous piece of shortwave energy which dove southeast from the northern Plains and into the southern-tier of the Ohio Valley before lifting northeast towards New England:

At the surface, a warm front was pushing north through Long Island Sound towards CT. As the warm front lifted north of CT during the early afternoon the airmass became warm and humid while the warm front result in rather strong low-level directional wind shear (an important ingredient needed for tornadoes). This image below (courtesy of The Weather Bureau) shows the surface set-up from 7:00 AM EDT October 3, 1979. At this time, the warm front was positioned south of CT with temperatures across the state only in the 50’s:

An area of low pressure at the surface developed and passed just west of CT with an occluded front just northwest of CT, warm front placed just north of the state, and a cold front moving into the state from NY. This placed CT in what is known as the triple point. The triple point is where the occluded front, warm front, and cold front intersect. While not always a certainty, this area can be favorable for severe thunderstorms; including tornadoes as an overlap of instability and wind shear is most likely to occur within this area. Below is an illustration of the triple point from meteorologist Jeff Haby (Image courtesy of meteorologist Haby – theweatherprediction.com):

During the early-to-mid afternoon, there reports of sun breaking out across northern CT which result in an increase in temperature along with instability. During the time a supercell thunderstorm was south of Long Island, heading north towards the CT Valley. There were reports of a funnel cloud as this moved over Long Island. 

As this storm moved north it moved through the CT River Valley. Due to the configuration of the valley, low-level wind shear was likely enhanced and strengthened with surface winds more southeast while winds a few thousand feet off the ground were more from the south-southwest. As this supercell moved into northern CT, it tapped into the stronger instability likely resulting in a strengthening mesocyclone which ultimately produced a violent tornado.

The tornado formed about 3:00 PM EDT Wednesday, October 3, 1979 causing significant destruction to the airfield, business, and residential buildings. Three people were unfortunately killed with several hundred more injured making this the deadliest tornado in CT since the 1878 Wallingford tornado. At one point, this tornado was the 6^th most costly U.S. tornado on record, causing $200 million in 1979 U.S. Dollars ($690 million in 2019 U.S. Dollars).

Some CT tornado facts:

·       Between 1950-2018 CT has had 105 confirmed tornadoes (yielding an average of about 1.5 per year).

·       The two most active years on record are 2018 and 1973 – both with 8 confirmed tornadoes.

·       Of the 8 confirmed tornadoes in 2018, two occurred during the month of October. These were the first two confirmed tornadoes during the month of October in CT since the 1979 tornado.

·       The most confirmed tornadoes in one day was 5; occurring on July 21, 2010.

·       CT has had two confirmed F4 tornadoes (October 3, 1979 and July 10, 1989). Note: The F-scale rating did not exist in 1878, but that was likely at least an F4 tornado.